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Arc calibrations come for two gratings (LR and MR) and two instrument arms (SW and LW), thus one may find the following abbreviations:

SSAL short wavelength spectroscopy arcs using the LR grating

SSAM short wavelength spectroscopy arcs using the MR grating

LSAL long wavelength spectroscopy arcs using the LR grating

LSAM long wavelength spectroscopy arcs using the MR grating

The isaacp arc recipe was considerably improved and was put in operation for data taken after 2003-11-20. The arc recipe produces two kind of coefficients: a) the wavelength dispersion coefficients (3 parameters) and b) the optical distortion in x-direction for the whole field of view (6 parameters).

The QC parameters for the wavelength solution are : QC.DISPC01, QC.DISPC02 and QC.DISPC03, where

The QC parameters of the optical distortion in y-direction are derived from a different kind of calibrations: startrace frames.

The LR grating recipe generates two products, one for the Ar lamp and one for the Xe lamp separately.
The MR grating recipe generates one product with lines of both lamps.

The pipeline recipe processes the arc frames in two parts. The first part is on the arc line detection and the correction of the optical distortion in x-direction. The second part is on the arc line identification via the arc line catalog and calculating the non-linear wavelength dispersion transformation.

- After arc lines have been detected the curvature is modeled by a polynomial and correct to get straight lines. At least three emission lines must be detected. The polynomial describes the optical distortion in x-direction only. The optical distortion correction in y-direction is not required in this calibration step. See startrace calibrations for details on the optical distortion in y-direction.

- As good practice the optical distortion coefficients are applied to five selected points in the FOV. These are the four detector quadrant centers (ul,ur, ll, lr) and the center of the detector (cc). These effective distortions are not stored in the DB. They are calculated on the fly, when the health check plot is updated.

arc line number

isaac_arc, qc_arcs_num

- the number of detected arc lines

number of arc lines with fwhm

isaac_arc, qc_arcs_numgood

- the number of detected arc line for which a fwhm could be calculated